This invention relates to stoves, especially but not exclusively
wood burning stoves, or stoves capable of burning wood properly. It is especially
but not exclusively applicable to stoves which have windows for viewing the fire
There is a growing realisation that burning wood is good
for the environment compared to burning fossil fuels. It is "carbon neutral" in
modern terminology, and wood has less embodied energy per unit weight than coal,
or oil, for example.
Burning wood can cause smoke and pollution. The hotter
the burn the less pollution there is. Combustion can be more complete/efficient
at hot temperatures, especially for particulates e.g. soot and smoke. Also, the
hotter the burn the less tars and residues, and even water from logs, condense in
the stove or chimney or flue. Burning fuel more completely is also good for energy
Our earlier patent
discloses a way of pre-heating air to improve combustion/achieve high
combustion temperatures in a stove, and of passing a wash of heated air over a glass
window in the door of the stove. The product made to that design is very successful.
People want to have less smoke produced by their stoves.
When there is a window in the door of the stove they want to be able to see the
flames/logs burning. If the window soots up too quickly this detracts from the experience/effect.
Our "airwash" system discussed in
helps to keep the window clear, as well as often making the stove suitable
for low emissions areas/smoke control geographic areas. By passing air over the
glass window in the door of the stove in
we help keep the window clear of discolouration. By pre-heating the air
that enters the fire-box through the grate we improve combustion, and by pre-heating,
the airwash air we also achieve more complete combustion and help to burn residues/particulates
in the vicinity of the window (as well as stopping them settling on the window).
A clear view of the fire through the window is achieved.
Some people want to heat water in a boiler in the fire-box
of a stove. Putting a boiler in a stove heats water, but reduces the combustion
temperature in the fire-box, causing less complete combustion, and causing the problems
associated with that. We have historically discouraged people from having boilers
in their stove because of the reduction in combustion temperature/increase in pollution/greater
tendency to cause the glass in the stove door to get dirty and obscure the view
of the fire.
According to an aspect the invention comprises a stove
having a grate, a fire-box above the grate, thermal insulation defining a back surface
of a fire-box space, and a boiler water chamber or heat exchanger at a back wall
of the stove at the level of the fire-box, and in which the insulation is disposed
between the fire-box space and at least a lower part of the water chamber or heat
exchanger that is adjacent the grate so as to provide thermal insulation between
the lower part of the fire-box space and the water chamber.
Preferably a pre-heating chamber for pre-heating air is
provided beneath an ash pan chamber of the stove and/or at side regions of an ash
pan chamber of the stove, an air delivery chamber or slot is provided to deliver
pre-heated air from the pre-heating chamber to the inside of a window of the stove,
and at least one pre-heated air communication channel(s) is/are provided communicating
the pre-heating chamber with the air delivery chamber or slot. The air communication
channel(s) is/are provided at the front wall of the stove.
We have realised that it is possible to have a boiler with
a stove, and in particular with the stove of
, without significantly increasing particulate pollution and/or increasing
the tendency for the glass in the stove door to get dirty. We have realised that
in prior art stoves the boiler is actually in the fire-box in direct contact with
the fuel being burned and the frames. This produces a fast heating performance in
the boiler - heat is efficiently transferred to water in the boiler and the heat
per unit of time that is transferred to the water in the boiler can be high. So
heavy use of hot water can be accommodated. However, having the boiler water chamber
directly in the fire-box, as one of the surfaces that constrains the fuel/fire,
reduces the temperature of combustion because of the high rate of heat extraction
from the fire-box to the water in the boiler (and then the external water pipework/tanks
outside of the boiler). This can result in incomplete combustion, sluggish response
from the fire in the stove to changes, and build up of residue in the flue way and
chimneys, and possibly in dirty venting windows
By having the boiler water chamber behind thermal insulation
at least in part, e.g. at the lower parts of the fire-box, we maintain a high combustion
temperature. It seems odd at first to insulate a boiler from the fire in the fire-box;
it is wanted that heat gets to the boiler. However, we have realised that what is
better, in order to maintain a high combustion temperature, is for heat that seeps
through the insulation should heat the water in the boiler, rather than heating
the air in the room after being transferred through the sides/back wall of the stove,
and/or for heat to be selectively taken from parts of the fire-box where combustion
does not occur to a great extent.
The "leaked" heat should be used, and/or heat that would
otherwise go up the flue.
This may reduce the rate of heat transfer to the water,
but we do not think that this is unacceptable.
Put another way, we do not put a heat exchanger in the
part of the fire-box where the majority of insulation takes place: we put it outside
of the actual fire-zone itself.
The insulation may extend from the level of the grate to
about halfway up the height of the fire-box space, from the grate to the top wall
of the stove, and the water chamber may extend from the base of the fire-box space
to a height that is more than insignificantly above the top of the insulation.
The insulation may comprise any suitable material that
has low thermal conductivity. The insulation may comprise any non-metal material,
preferably with thermal conductivity less than the thermal conductivity of metal.
The insulation may comprise an air space between two layers of material. The insulaton
may be a solid material.
The thermal conductivity of the insulation may be about
0.05 W/mK to about 1 W/mK at the temperature range of between about 200°C to
about 600°C. The thermal conductivity of the insulation may be about 0.10 W/mK
to about 0.30 W/mK at the temperature range of between about 200°C to about
600°C. The thermal conductivity of the insulation may be about 0,14 W/mK at
the temperature of about 400°C.
The insulation may comprise at least one refractory brick
or at least one insulating board. The insulation may comprise any of the group comprising
ceramic, mineral wool, glass fiber, cement, mica, diatomaceous earth, silica and
The insulation may be about 5 mm thick to about 110 mm
thick, or about 10 mm thick to about 100mm thick. The insulation may be about 20
to about 40 mm thick. The insulation may be about 30 mm thick. The insulation may
vary in thickness with regions of relatively thicker insulation and regions of relatively
Each of the ranges and values of insulation material thickness
given, combined with one of the ranges or values of thermal conductivity given,
will produce a range or value of thermal resistance in units of m3K/W.
The insulation may be of any material and thickness which has those ranges or values
of thermal insulation.
The water chamber may extend upwards insulated by insulation
for at least about R of the fire-box height.
In some embodiments we can put the boiler, or a part of
the boiler, at the top of a stove housing, typically above a baffle. Again, not
much/practically no combustion occurs there: combustion is largely complete by then,
and so removing heat from a region where little combustion is taking place anyway
is not so bad. Indeed, it is good for the point of view of thermal efficiency of
the stove as a whole.
A deflector plate or baffle may be provided part way up
the height of the fire-box space, extending away from the back of the fire-box space,
and there may be insulation at the back of the fire-box space from the level of
the grate up to the level of the rear of the deflector plate or baffle, or to about
that level, and significantly less insulation, or no insulation, above about the
level of the back of the deflection plate or baffle.
The stove may comprise a housing carcass having front,
back and side walls, and the back wall may define a boiler water chamber receiving
aperture, and a boiler unit, comprising the boiler water chamber and an associated
mounting formation, may be mounted to the back wall with the boiler water chamber
extending through the boiler water chamber receiving aperture, the mounting formation
mounting the boiler unit to the back wall. The mounting formation may be releasably
fastened to, or clamped to, the back wall of the carcass by releasable mechanical
fasteners. The aperture in the back wall may comprise substantially the whole of
the back wall above the grate, the aperture being surrounded by a back wall mounting
flange to which the mounting formation is affixed. The mounting formation may comprise
a mounting flange extending around the periphery of the boiler water chamber.
The water chamber may have an upright portion and a laterally
projecting portion extending into the fire-box space, away from the back wall portion.
The projecting portion may extend for about R to about S of the back-to-front
depth of the fire-box space.
The boiler water chamber may extend upwards from at least
about the level of the grate to the top of the stove, or nearly so.
There may be a water inlet conduit at or near to the bottom
of the upright extent of the water chamber and a water outlet at or near to the
top of the upright extent of the water chamber.
According to another aspect the invention comprises a method
of manufacturing a stove with a boiler which maintains a higher combustion temperature
in the fire-box of the stove, the method comprising positioning a boiler chamber
outside of the fire-box itself and insulated from at least part of the fire-box
There may be a back wall aperture in the back wall of the
stove and the method may comprise introducing a boiler unit into the stove from
the outside of the stove through the back wall aperture, and fixing the boiler unit
to the back wall of the stove.
In some embodiments the boiler water chamber is welded,
or otherwise attached, permanently to the stove housing. However, it is preferred
to have the boiler chamber attached to a plate defining an exterior surface of the
stove housing, and to have that plate removable from the stove housing. This can
help in repair or maintenance. The back wall of the stove is our preferred place
for such a removable unit.
In some embodiments the boiler water chamber has a substantial
vertical/upright extent, typically for substantially the full height of the fire-box
from the grate to the top wall of the stove. This enables the water inlet to the
boiler water chamber to be well spaced vertically from the water outlet from the
boiler water chamber, which can help with thermal siphoning water flow in the boiler
The water chamber may have an upright region and a projecting
region extending into the stove, away from the upright region. The projecting region
and the upright region may be generally at right angles to each other.
According to another aspect of the present invention there
is provided a domestic heating stove or cooking range the body or casing of which
incorporates a removeable panel or an open section to facilitate the addition of
a water boiler.
The body or fire-box of the stove is lined with refractory
brick or insulating board. The body of the stove or door of the stove or range incorporates
a means of distributing air over the glass viewing windows to prevent soot deposits
and provide clear vision of the fire.
According to the present invention the boiler or water
jacket does not form a wall or panel in direct contact with the fire. The boiler
or water jacket is separated from direct contact with the fire by means of refractory
bricks or insulating boards, thus the heat transfer is slower than a conventional
direct contact system. However the water container or boiler is less prone to cool
the combustion, high efficiency is maintained offering cleaner chimneys and reduced
air pollution. The hot fire will not be sluggish and a clear fire view can be maintained
by pre-heated air distribution over the fire viewing door or window.
Condensation often forms on the cool surface of a conventional
boiler. Corrosion of the boiler is reduced by insulating the fire from the boiler
A stove or range may be provided in which the boiler can
be added or removed by providing an absent or removable stove body section enabling
the boiler to be in close contact with refractory bricks or lining panels maintaining
hot combustion and reducing condensation by direct contact between the fire and
cold boiler surfaces.
Embodiments of the invention will now be discussed by way
of example only, with reference to the accompanying Figures, of which:-
Figure 1 is a front view of a prior art stove (without its door);
Figure 2 is a side view of the prior art stove of Figure 1 showing some internal
structure and including a door;
Figure 3 is a perspective view of the prior art stove of Figure 1 (without
Figure 4 is a view similar to that of Figure 2, but showing airflow in more
Figure 5 shows a schematic perspective view of a new stove with the door
and ash pan removed for clarity;
Figure 6 shows a schematic side cross-section of the stove of Figure 5, with
the door and ash pan shown;
Figure 7 shows a schematic view of a boiler chamber of the stove of Figure
5, with some associated insulation material;
Figures 8 and 9 show the boiler chamber in more detail;
Figure 10 shows a view from the rear, and outside of the stove, of a boiler
chamber unit disassembled from the stove;
Figure 11 shows detail of insulation layers provided at the sides and back
of the fire-box of the stove of Figure 5; and
Figure 12 shows schematic details of the back wall of the stove of Figure
Figures 1 to 4 show our existing, prior art, stove discussed
, the contents of which are hereby incorporated by reference. The Patent
Law of some countries do not allow incorporation by reference and so a description
of the prior art stove follows in this patent application itself. The disclosure
will be useful in understanding the structure of the example embodiment of Figures
5 to 12 since that stove has been developed from the prior art stove of Figure 1
A solid fuel stove 1 (typically a wood burning stove) is
shown in Figures 1 to 4 of the drawings and has a main body 2 standing on legs 3;
a fire-box 4 inside the stove 1 in its upper portion; an ash chamber 5 inside the
stove 1 below the fire-box 4; and pre-heating means 6 inside the stove 1 below the
ash-chamber 5 and extending up the inside of a front panel 7 of the stove 1. A dividing
wall 17' separates the fire box from the ash chamber, and a grate 19 is provided
in the dividing wall.
There is a large door aperture 8 in the upper part of the
front panel 7 of the stove 1 which provides access into the fire-box 4 to replace
fuel (not shown).
In the lower part of the front panel 7 is a small aperture
10 beneath the large aperture 8. The small aperture 10 provides access into the
ash-chamber 5 to empty ash created by the combustion of fuel.
Both of the apertures are closed by a door 35 which is
mounted on hinge lugs 9 fixed to the front panel 7 of the stove 1. The door 35 has
a transparent window 36 and an air inlet 37 which can allow air to enter the ash
chamber. The air inlet 37 is controlled by aperture control means, such as a "spinner"
38, which may be thermostat controlled. A sealing band 39 extends around the peripheral
edge of the door and seals the closed door to the front panel 7 of the body.
The fire-box 4 is in the upper portion of the stove 1 and
is formed by the front, back, and side walls of the box 2, and by the dividing wall
A back wall 11 of the fire-box 4 is protected from the
heat of the fire and the hot solid fuel by an insulating/heat resisting layer 12.
Insulation is also provided on the side walls of the fire box.
Above the insulating/heat resistant layer of the back wall
11 is an exhaust aperture 13 through which the exhaust gases of the fire pass on
the way to a chimney (not shown). Removably mounted on the back wall 11 between
the insulating/heat resisting layer 12 and the exhaust aperture is a deflection
plate 14, which extends across the entire width of the fire-box 4 and rests on the
insulation on the side walls of the fire-box. The deflection plate 14 stops short
of the door 35 and so provides a gap 16 between itself and the front panel of the
stove. The deflection plate is inclined, and the edge at the back wall 11 of the
fire-box 4 is at a level slightly below the top of the large aperture 8 while the
front free edge 15 is at a level slightly above the top of the large aperture 8.
As described earlier, the bottom of the fire-box 17 has
a dividing wall 17'. The dividing wall 17' is provided with an ash aperture 18 which
is covered by a removable grate 19 on which solid fuel can stand. The grate 19 also
serves the purpose of allowing communication between the fire-box 4 and the ash-chamber
5 so that waste ash can fall into the ash-chamber 5 and air can rise up through
the grate to feed the fire from beneath,
The ash-chamber 5 has two apertures, the small aperture
10 and the waste aperture 18 both of which have been mentioned previously. The ash-chamber
5 collects the waste that falls through the waste aperture 18 in a collection pan
20 which sits beneath the grate 19. The collection pan 20 can be removed from the
stove 1 through the small aperture 10 in order to empty the collection pan 20 of
Beneath the ash-chamber 5, occupying a space across the
width and depth of the stove 1 is an air chamber 21 which constitutes part of the
pre-heating means 6. The air chamber 21 is at the bottom of the stove 1 inside the
body 2. In the bottom of the body 2 is an air aperture 23 which communicates the
air chamber 21 with air outside of the stove 1. A regulator plate 24 is slidably
movable to cover, partially cover, or uncover the air aperture 23. The regulator
plate 24 is moved by a knob 25 which is attached to the plate by a rod 26. Pulling
or pushing the knob 25 in or out slides the regulator plate 24 in relation to the
air aperture 23.
Air delivery means 27 is provided above the large aperture
8, running across the front panel 7 in the inside of the box 2. The air delivery
means 27 is a passage or chamber that has an exit point or slot 28 along its bottom.
The slot 28 is provided next to the top of the door and the top of the large aperture
The air chamber 21 and the air delivery means 27 are connected
by communication channels or passageways 30. The passageways 30 comprise two conduits
30' that run up either side of the large aperture 8 and cut through the dividing
wall 17' , There is no direct communication between the passageways 30 and the fire
box, only through the slot 28, A continuous air path is formed from the outside
of the stove (beneath the stove) to the fire-box 4, through the air aperture 23,
along the flat bed of the air chamber 21, up the passageways 30, into the air delivery
means 27 and through the slot 28 and into the fire-box 4. This path is shown by
the arrows A of Figures 1 and 2, It will be noted that the conduits 30' pass through
the dividing wall 17'.
The stove 1 is supported by legs 3 for its base 31 to be
standing above the level of the floor in order for air to be supplied readily to
the air aperture 23
In operation the fire-box 4 is loaded through the large
aperture 8 with solid fuel which rests on the grate 19. The fuel is ignited and
once it is burning steadily the door is closed. Until this point the fire was fed
by air entering through the large aperture 8, as well as possibly air through the
air intake aperture 23 and air through the spinner 38. The knob 25 is pulled out
so that the aperture 23 is open to its fullest extent. The fire draws air to be
combusted and air is sucked through the air aperture 23 into the air chamber 21
to rise up the passageway 30 and into the air delivery means 27 and out of he slot
28 into the fire-box. In this way air is drawn through the system comprising the
During burning, fuel becomes spent and the ash that is
created falls into the collection pan 20 in the ash-chamber 5. The ash is hot and
the bottom 31 of the ash-chamber 5 becomes hot. The burning of the fuel heats the
fire-box 4 considerably and the walls and the connecting means 5 become hot. The
hot air from the combustion process rises upwards. The exhaust air hits the deflection
plate 14 and as the air continues to rise, it flows along the deflection plate 14
towards the front panel 7. As the exhaust air passes the front edge 15 of the deflection
plate, it overshoots and plays over the rear face 29 of the air supply means 27.
This may cause a draft in the region of the slot 28. Furthermore, pre-heated air
is leaving the slot 28 in a downwards direction. The two airflows mix,
Figure 4 illustrates schematically the airflow which is
believed to occur in the fire box. There are three main inputs of air: air rising
from the fire itself (referenced as B), rising air deflected by the plate 14 (referenced
as C), and pre-heated air moving downwards from slot 28 (referenced as D). As the
deflected air C meets the pre-heated air D at the top of the door 35 they mix and
cause turbulence E at the region of the window 36. This turbulence pushes air, and
more importantly soot and smoke F rising from the fire away from the window and
keeps the window cleaner than in conventional fires, The introduction of pre-heated
air also enables a higher temperature to be achieved, which results in less soot
Uncombusted air passing through the pre-heating means 22
is warmed firstly by contacting the bottom 31 of the ash-chamber 5. The draw on
air for combustion takes the air up the connecting conduits 30' which are by now
hot an the air is heated further. The air receives further pre-heating in passing
through the slot 28 and some mixing occurs with the rising and escaping air rising
from the deflection plate 14, The draft and/or turbulence caused by the exhaust
gases in the region of the front edge 15 of plate 14 may draw air from slot 28,
or assist in doing so.
Once the fire in the stove is fully burning, it can be
controlled by adjusting the knob 25 which controls the amount of air entering into
the fire-box 4.
It is an advantage of the stove that it is constructed
to intake an air supply from the room. In this way it is very simple to install
and it does not require a conduit to have been previously installed in the house.
The only connection that needs to be made is to connect the flue of the stove to
a suitable system to deal with exhaust gases, for example a chimney. Otherwise all
that is required is a flat area on which the legs of the stove can stand. A hearth
area would be suitable.
In addition, the stove is very compact since all of its
elements with the exception of the flue can be housed in a small box.
The fire is clean, can be seen through the window which does not readily dirty,
is efficient, and has a relatively high air flow for its compact size.
The "air-wash" system of slot 28, passageways 30, and air-chamber
21 help to keep the window clean.
Figures 5 to 12 show our new stove 101. It has a similar
construction to that of Figures 1 to 4, except that the airwash system now has a
chamber down both sides of the grate and along the back of the grate (as well as
below the ash-pan chamber, and except for a boiler arrangement (the subject of this
Figure 5 shows stove 101 having a front wall 102, a back
wall 103, and opposed side walls J.04 and 105, and a top wall 106. The stove has
a boiler water chamber 107 shown largely in dotted outline provided at the back
wall, and a grate 108 in a dividing wall 109 separating a fire-box 110 from an ash-pan
chamber 111. A pre-heating chamber 112 (best seen in Figure 6) extends beneath the
ash-pan chamber 111. An air delivering slot or channel 114 extends above a door
aperture 115 and is intended to deliver pre-heated airwash air down over the inside
surface of a glass window 116 of a door 117 (shown in Figure 6). Upright corner-post
air communication channels 118 and 119 extend from the passage or chamber 112 beneath
the ash chamber 111 to the above-door air delivery channel 114. They help to provide
rigidity at the front of the stove. The stove is made from sheet metal that has
been bent and welded. Insulation 120, such as firebricks, or refractory thermal
insulation, has been omitted from Figure 5 for clarity, but is shown in Figure 6
and in Figure 110. The insulation 120 has side portion 123 which extends along,
and defines a boundary at, the bank of the fire-box space 110.
A deflector plate or baffle 124 is also not shown in Figure
5, but is shown in Figure 6. This rests on the insulation 121, 122, and 123. It
may be fixed in place (e.g. with adhesive). The baffle plate 124 may be solid, or
may provide an air supply to the fire-box space 110 (in which case it may have an
air supply channel extending to the outside of the stove, for example to the back
Figure 6 also shows an ash-pan 126, beneath the grate 108.
An air inlet 127, with a manual control 128, is provided
to control the supply of air to the chamber 112. Another air supply, with manual
control, is provided (not shown) to provide a controllable air supply to the ash-pan
chamber, under the grate.
The stove 101 rests on legs 130 lifting it about 3 inches
(8cm) off a base surface upon which it stands. This second air control is often
provided in the door of the stove.
The boiler water chamber 107 is shown in Figures 6 to 10,
Figures 8 and 9 showing it on its side. The boiler chamber is provided as part of
a boiler unit 140 comprising a back wall mounting plate 141, an L-shaped, bent,
internal boiler water chamber - defining wall 142, a projecting wall 143 projecting
away from the mounting plate 141, and side plates 144 and 145.
The water chamber 107 has a first, generally upright, portion
146 which extends up the back wall 103 of the stove, and an internally projecting
portion 147 which extends into the housing of the stove, into a space 148 above
the baffle 124. A flue aperture 149 is provided in the upright portion 146, and
is provided by welding a pipe 150 to aperture-defining surfaces of the walls 141
The walls 144 and 145 may be folded portions of wall 143,
or they may be separate components. The walls 144 and 145 are welded to L-shaped
bent wall 142, and to projecting wall 143 and to upright wall 141. Bent L-shaped
wall 142 is also welded to upright wall 141 and to projecting wall 143. Wall 143
is welded to wall 141. Together, the pipe 150, and the walls 141, 142, 143, 144
and 145 define an L-shaped boiler water chamber space 151.
Two water inlets 152 and 153 are provided at the bottom
of the upright portion 146. Two water outlets 154 and 155 are provided at the top
of the upright portion 146.
Figure 12 illustrates schematically the back wall 103 of
the stove viewed from the front of the stove. A large boiler unit-receiving aperture
160 is provided in the back wall 103, defined by a mounting flange 161 surrounding
the aperture. Holes 162 are shown in the flange 161. These holes 162 have welded
in them (not shown) captive bolts projecting outwards/backwards of the stove.
Figure 12 also shows that the ash-pan chamber 111 has airwash
air (to be delivered to the passageway 114 above the door) pre-heating channels
163 and 164 to either side of the ash-pan chamber, and airwash air pre-heating channel
165 at the back of the ash chamber, all in communication with the upright channels
118 and 119 shown in Figure 5.
To manufacture the stove 101 the unit 140 is inserted into
the internal space within the carcass 102 from the back of the stove through the
aperture 160. The mounting plate 141 has a peripheral mounting portion, or flange
170. surrounding the region of plate 141 which part-defines chamber space 151. Holes
171 are provided in the mounting portion 170 which marry up with the projecting
captive bolts mounted in holes 162 of the back wall 103. The mounting portion 170
is fitted over the bolts and nuts are then put on its projecting screw threaded
bolts, and the nuts tightened.
A gasket/seal (not shown) is provided surrounding the aperture
160, clamped between the flange 161 and the flange 170.
To install the stove in a domestic kitchen, or the like,
pipe 150 is connected to a flue pipe. Water inlet pipes of a hot water system are
connected to inlets 152, 153, and water outlet pipes of the hot water system are
connected to the outlets 154, 155.
Figure 11 shows schematic detail of the insulation 120,
121. 123, and shows the flue aperture 149 disposed above the top of the insulation.
The stove has not had the combustion temperature of the
fire units firebox space reduced significantly in comparison with the stove of Figures
1 to 4 since the insulation 120 prevents too fast heat transfer to the water in
the boiler water chamber. The lower part of the water chamber, adjacent the grate
where the fire is burning, and where most combustion takes place, is insulated.
Higher up, away from the wood that is burning, the water chamber is uninsulated
(or we could provide less insulation). This permits heat to be taken out of the
space at the top of the fire-box, above the baffle. This heat previously, in the
main, leaked away to the room in which the stove was located and/or went up the
Reducing flue gas temperatures by extracting heat using
a boiler there is not detriment to the hot combustion effect we want. It may even
help to achieve better thermal efficiency figures.
We have realised that it is not simply a question of choosing
between on the one hand high combustion temperatures and low pollution, and a window
that stays clean for longer, but no boiler, and on the other hand having a boiler
but sacrificing high combustion temperatures and having a window that gets dirtier.
We can have both, if we are careful where in the fire-box we extract heat and insulate
the near-grate part of the fire-box to retain heat.
An unexpected additional synergistic benefit of the invention
is that we can position our now stove closer to combustible surfaces. Current UK
legislation requires a stove to be about 450 mm or so away from combustible material
(such as a plasterboard wall). This is a big gap to have behind a stove placed in
front of a wall (e.g. in a new house/partition wall of plasterboard, or even a plasterboard-clad
stone or brick wall).
However, the regulations allow the stove to be closer (about
150 mm away from the material) if the temperature of the outside of the stove is
not more than 65°C above ambient temperature.
Tests have shown that our new stove has a back wall temperature
which is not more than 65°C above ambient, and so we can position the stove
closer to the wall behind it. The back wall of our stove may have, in use, a temperature
of about 50° or 60°C, or perhaps 70°C, or even 80°C. It should
not exceed about 85°C.
A further spin-off benefit is that users can now have a
bigger stove, with a bigger window so that they can see more of the fire burning,
than before. Previously, the heat emitted by the stove all went to the room (or
up the flue) and thus meant that people had to accept smaller stoves (high temperature
combustion clean-fire stoves) in order to avoid sweltering temperatures in their
kitchen/other stove-containing room. Now, the boiler will take out some heat, so
a bigger stove (possibly with a better view of the fire) is possible.
The boiler is arranged to take out about R to
2/3 of the heat generated by the stove, preferably between
about and S of the heat generated, or between R and S of the heat
We envisage a stove which is primarily for space-heating
the room, looks good and has a good view of the fire burning, and which burns clean
using high temperature combustion, but also heats some hot water, (rather than central
heating boiler which has modest temperature combustion and being primarily a central
heating boiler which also heats a room directly). Our stove may have a towel rail,
which will get hot/warm, and the top of the stove (if it has a flat top) will typically
still get hot enough to boil a kettle.
The simple design of our boiler unit, removably inserted
from the back of the stove, complements the design of the earlier stove where the
air-wash channels are at the front. We may make our earlier stove 20, 30. or 40
mm or so deeper so that the fire-box remains the same depth even with the boiler
unit projecting to the back of the insulating material. This will enable the same
refractory material inserts to be used, and the same baffle, to be used as we use
for the boiler-less stove.
The viewing window for the fire may not be present at all
(but usually will). In addition to, or instead of, a window in the door one or more
other fire-viewing windows may be provided (e.g. in side walls).
The airwash pre-heating channels need not be in the front
of the carcass by the door; they could for example be in the door itself.
The standard test for measuring the efficiency of stoves
is EN 13240. This measures the calorific value of the fuel burned, the temperature
of the flue gases, and the levels of carbon monoxide, carbon dioxide and oxygen
in the flue gases to produce an efficiency figure. Our new stove performs well.
The boiler water chamber may not project laterally into
the fire-box. We prefer that it does, but it may not be essential.
The boiler water chamber may not extend down to the level
of the grate. We prefer that it does. This increases the vertical height between
the water inlet and outlet, improving circulation of water in the hot water system
coupled to the stove/in the water chamber. The boiler water chamber, or water jacket,
may conceivably be provided solely above the baffle, but we strongly prefer providing
it with at least some vertical component.
We may provide air convection panels at the sides of the
stove to provide air-insulation of the sides/cooler to touch side surfaces to the
stove. The convection panels may effectively trap/partially trap a body of air between
them and the side walls of the main carcass.
The boiler unit may include, or be associated with, a thermostat
controller to control water flow through the water chamber.